1. Field of the Invention
This invention relates generally to electronic systems and methods for locating buried or otherwise inaccessible pipes and other conduits, cables, conductors and inserted transmitters, and more specifically to sonde and line locators for detecting an electromagnetic signal emissions.
2. Description of the Related Art
There are many situations where is it desirable to locate buried utilities such as pipes and cables. For example, prior to starting any new construction that involves excavation, it is important to locate existing underground utilities such as underground power lines, gas lines, phone lines, fiber optic cable conduits, CATV cables, sprinkler control wiring, water pipes, sewer pipes, etc., collectively and individually referred to hereinafter as “utilities” or “objects.” As used herein the term “buried” refers not only to objects below the surface of the ground, but in addition, to objects located inside walls, between floors in multi-story buildings or cast into concrete slabs, etc. If a backhoe or other excavation equipment hits a high voltage line or a gas line, serious injury and property damage may result. Severing water mains and sewer lines leads to messy cleanups. The destruction of power and data cables can seriously disrupt the comfort and convenience of residents and cost businesses huge financial losses.
Buried objects can be located by sensing an electromagnetic signal emitted by the same. Some cables such as power lines are already energized and emit their own long cylindrical electromagnetic field. Location of other conductive lines necessitates their energizing with an outside electrical source having a frequency typically in a range of approximately 50 Hz to 500 kHz. Location of buried long conductors is often referred to as “line tracing.”
A sonde (also called a transmitter, beacon or duct probe) typically includes a coil of wire wrapped around a ferromagnetic core. The coil is energized with a standard electrical source at a desired frequency, typically in a range of approximately 50 Hz to 500 kHz. The sonde may be attached to a push cable or line or it may be self-contained so that it can be flushed through a conduit. A sonde generates a more complex electromagnetic field than that produced by an energized line. However, a sonde can be localized to a single point. A typical low frequency sonde does not strongly couple to other objects and is thereby unlikely to produce complex interfering fields that may occur during the tracing. The term “buried objects” as used herein also includes sondes and buried locatable markers such as marker balls.
Besides locating buried objects before excavation, it is further desirable to determine the depth of the objects. This is generally done by measuring the difference in field strength at two locations.
Ground penetrating radar (GPR) may be used to locate non-conductive object underground. Using GPR in association with accurate positional information provided by a mapping locating instrument can provide additional functionality as measurements from multiple known positions may be compared and analyzed to form an image of underground structures.
As may be appreciated from the above discussion, both arts are replete with suggested methods and systems for improving buried object and utility locator operation. In fact, there are several different fundamental physical approaches to the problems, each of which has strengths and weaknesses in different situations. The introduction of inexpensive processing power and complex software systems has made it possible for the first time to improve locator performance using a graphical user interface (GUI) to present data obtained from a plurality of sensors, as disclosed in the above-cited patent applications incorporated herein by reference. Portable locators that heretofore have been developed offer limited functionality insufficient for quickly and accurately locating buried utilities. There is still a clearly-felt need in the art for a portable locator system that can operate in any of several different operator-electable realms, such as the acoustic, electromagnetic and optical realms, to permit effective buried object location under a wide range of circumstances without obliging the operator to maintain and transport numbers of different systems and apparatus. These unresolved problems and deficiencies are clearly felt in the art and are solved by this invention in the manner described below.